CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
CASH FLOWS FROM OPERATING ACTIVITIES
Net income	$ 49,487	$ 54,252
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	7,880	6,849
Stock-based compensation	9,482	8,688
Provision for excess and obsolete inventories	899	1,321
Deferred income taxes	(3,651)	(5,765)
Income tax benefit associated with stock option exercises	2,749	1,924
Excess tax benefit from stock-based compensation	(679)	(3,360)
Amortization of premium on investments, net	606	849
Other operating activities	659	389
Changes in assets and liabilities, net of effect of acquisition:
Accounts receivable, net	5,008	246
Inventory, net	(8,230)	(5,390)
Current and other assets	(1,218)	(408)
Accounts payable	(3,854)	(8,883)
Accrued liabilities	(559)	(6,762)
Income taxes	1,445	12,630
Cash provided by operating activities	60,024	56,580
CASH FLOWS FROM INVESTING ACTIVITIES
Proceeds from sales of short-term investments	25,057	66,060
Proceeds from maturities of short-term investments	60,890	83,108
Purchase of short-term investments	(65,411)	(88,783)
Proceeds from sales of long-term investments	2,000	4,936
Purchase of long-term investments	(33,951)	(45,194)
Acquisition, net of cash acquired	(1,723)	0
Capital expenditures and other assets	(21,526)	(10,044)
Cash (used for) provided by investing activities	(34,664)	10,083
CASH FLOWS FROM FINANCING ACTIVITIES
Repurchase of common stock	(19,930)	(184,067)
Equity forward contract related to accelerated share repurchase program	0	(15,000)
Proceeds from sale of treasury stock	2,485	2,519
Proceeds from issuance of common stock	9,403	16,664
Proceeds from revolving line of credit	18,000	17,500
Repayments of revolving line of credit	(26,000)	0
Payment of cash dividends	(8,490)	(4,720)
Employees' tax withheld and paid for restricted stock and restricted stock units	(1,729)	(880)
Excess tax benefit from stock-based compensation	679	3,360
Cash used for financing activities	(25,582)	(164,624)
Effect of exchange rate changes on cash and cash equivalents	(1,184)	(1,037)
Net decrease in cash and cash equivalents	(1,406)	(98,998)
Cash and cash equivalents at beginning of period	209,335	284,375
Cash and cash equivalents at end of period	$ 207,929	$ 185,377